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Enter Title Here CORE Metadata, citation and similar papers at core.ac.uk Provided by UM Digital Repository International Journal of Mechanical and Materials Engineering (IJMME), Vol.5 (2010), No.2, 163-170. REYNOLDS AND PRANDTL NUMBERS EFFECTS ON MHD MIXED CONVECTION IN A LID-DRIVEN CAVITY ALONG WITH JOULE HEATING AND A CENTERED HEAT CONDUCTING CIRCULAR BLOCK M. M. Rahman1, M. M. Billah2, M. A. H. Mamun 3, R. Saidur4 and M. Hasanuzzaman4 1Department of Mathematics 1Bangladesh University of Engineering and Technology (BUET), Dhaka-1000, Bangladesh 2Department of Arts and Sciences, Ahsanullah University of Science and Technology (AUST), Dhaka, Bangladesh 3The Institute of Ocean Energy, Saga University, Japan 4Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia Email: [email protected] Received 20 May 2010, Accepted 29 July 2010 ABSTRACT Nu average Nusselt number p dimensional pressure (Nm-2) The fluid flows and heat transfer induced by the combined P dimensionless pressure effects of mechanically driven lid and buoyancy force Pr Prandtl number within a rectangular cavity is investigated in this paper Ra Rayleigh number numerically. The horizontal walls of the enclosure are Re Reynolds number insulted while the right vertical wall is maintained at a Ri Richardson number uniform temperature higher than the left vertical wall. In T dimensional temperature(K) addition, it contains a heat conducting horizontal circular ∆T temperature difference (K) block in its centre. The governing equations for the problem u, v dimensional velocity components (ms-1) are first transformed into a non-dimensional form and the U, V dimensionless velocity components resulting nonlinear system of partial differential equations U0 lid velocity are solved by using the finite element formulation based on V cavity volume (m3) the Galerkin method of weighted residuals. The analysis is x, y Cartesian coordinates (m) conducted by observing the variations of streamlines and X, Y dimensionless cartesian coordinates isotherms for different Reynolds number and Prandtl number ranging from 50 to 200 and from 0.071 to 3.0 Greek symbols respectively. The results indicated that both the streamlines α thermal diffusivity (m2s-1) and isotherms strongly depend on the Reynolds number and β thermal expansion coefficient (K-1) Prandtl number. Moreover, the results of this investigation ν kinematic viscosity (m2s-1) are also illustrated by the variations of average Nusselt θ dimensionless temperature number on the heated surface and average fluid temperature μ dynamic viscosity (m2s-1) in the enclosure. ρ density of the fluid (kgm-3) -1 -1 Keywords: Mixed convection, Galerkin method, Circular σ fluid electrical conductivity (Ω .m ) block and Enclosure. ψ stream function Subscripts NOMENCLUTURE av average 2 B0 magnetic induction (Wb/m ) h heated wall Cp Specific heat of fluid at constant pressure c cold wall D block of diameter s solid -2 g gravitational acceleration (ms ) Gr Grashof number h convective heat transfer coefficient(Wm–2K–1) 1. INTRODUCTION Ha Hartmann number 1.1 Literature Review J Joule heating parameter -1 -1 kf thermal conductivity of the fluid (Wm K ) Flow and heat transfer phenomena in lid-driven enclosures -1 -1 ks thermal conductivity of the solid (Wm K ) caused by the conjugate effect of buoyancy and shear forces. K solid fluid thermal conductivity ratio Mixed convection flow and heat transfer in lid-driven L length of the cavity (m) enclosures have been receiving a considerable attention in the literature. Conjugate mixed convection heat transfer has 163 possible applications in many engineering and natural configuration the isothermal sidewalls of the cavity were processes. Such applications include cooling of electronic moving downwards with uniform velocity while the top wall devices, lubrication technologies, drying technologies, food was adiabatic. Oztop and Dagtekin (2004) investigated processing, and flow and heat transfer in solar ponds, numerically steady state two-dimensional mixed convection thermal –hydraulics of nuclear reactors etc. Flow and heat problem in a vertical two-sided lid-driven differentially transfer from obstructed enclosures are often encountered in heated square cavity. many engineering applications to enhance heat transfer such A combined free and forced convection flow of an as micro-electronic device, flat plate solar collectors, and electrically conducting fluid in cavities in the presence of a flat-plate condensers in refrigerator etc. This kind of magnetic field is of special technical significance because of problems was investigated mostly for the case of natural its frequent occurrence in many industrial applications such convection in enclosures. Roychowdhury et al. (2002) as geothermal reservoirs, cooling of nuclear reactors, analyzed the natural convective flow and heat transfer thermal insulations and petroleum reservoirs. These types of features for a heated cylinder kept in a square enclosure with problems also arise in electronic packages, microelectronic different thermal boundary conditions. Dong and Li (2004) devices during their operations. Garandet et al. (1992) and Hasanuzzaman et al. (2007) studied conjugate of natural studied natural convection heat transfer in a rectangular convection and conduction in a complicated enclosure. The enclosure with a transverse magnetic field. Rudraiah et al. authors investigated the influences of material character, (1995a) investigated the effect of surface tension on geometrical shape and Rayleigh number on the heat transfer buoyancy driven flow of an electrically conducting fluid in a in overall concerned region and concluded that the flow and rectangular cavity in the presence of a vertical transverse heat transfer increase with the increase of thermal magnetic field to see how this force damps hydrodynamic conductivity in the solid region; both geometric shape and movements. At the same time, Rudraiah et al. (1995b) also Rayleigh number affect the overall flow and heat transfer studied the effect of a magnetic field on free convection in a significantly. Hasanuzzaman et al. (2009) investigated the rectangular enclosure. The problem of unsteady laminar nature convection in closed cavity of refrigerator. Braga and combined forced and free convection flow and heat transfer Lemos (2005) numerically studied steady laminar natural of an electrically conducting and heat generating or convection within a square cavity filled with a fixed amount absorbing fluid in a vertical lid-driven cavity in the presence of conducting solid material consisting of either circular or of a magnetic field was formulated by Chamkha (2002). square obstacles. The authors showed that the average Recently, Rahman et al. (2009a) studied MHD mixed Nusselt number for cylindrical rods is slightly lower than convection around a heat conducting horizontal circular those for square rods. Lee and Ha (2005) investigated cylinder placed at the center of a rectangular cavity along natural convection in a horizontal layer of fluid with a with joule heating. Very recent, the effect of a heat conducting body in the interior, using an accurate and conducting horizontal circular cylinder on MHD mixed efficient Chebyshev spectral collocation approach. Later on, convection in a lid-driven cavity along with joule heating is the same authors Lee and Ha (2006) also studied natural investigated by Rahman et al. (2009b). The authors convection in horizontal layer of fluid with heat generating concluded the streamlines and isotherms strongly depend on conducting body in the interior. Kumar and Dalal (2006) the size and locations of the inner cylinder, but the thermal studied natural convection around a tilled heated square conductivity of the cylinder has significant effect only on cylinder kept in an enclosure in the range of 103 ≤ Ra ≤ 106. the isothermal lines. The authors reported detailed flow and heat transfer features for two different thermal boundary conditions and found 1.2 Objectives of the Present Study that the uniform wall temperature heating is quantitatively In this paper, the effect of Reynolds and Prandtl number on different from the uniform wall heat flux heating. MHD mixed convection in a lid-driven rectangular cavity The cavity with moving lid has the most important along with a heat conducting circular block is to analyze application for these heat transfer mechanism, which is seen using Finite Element technique. From the literature review it in cooling of electronic chips, solar energy collection and is clearly seen that no work has been paid on such research food industry etc. Numerical analysis of these kinds of interest. systems can be found in many literatures. Moallemi and Jang (1992) investigated mixed convective flow in a bottom 2. PHYSICAL DOMAIN heated square lid-driven cavity. The authors studied the The configuration under study with the system of co- effect of Prandtl number on the flow and heat transfer ordinate is sketched in Figure 1. Fluid flows and heat process. They found that the effects of buoyancy are more transfer modeled in a two-dimensional rectangular lid- pronounced for higher values of Prandtl number and also driven cavity of length L with a heat conducting horizontal derived a correlation for the average Nusselt number in circular block of diameter D = 0.2, placed at the centre of terms of the Prandtl number, Reynolds number and the cavity. The left wall of the cavity is set to move upward Richardson number. Aydin and Yang
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